5000 Synapses in the Width of a Hair

That’s the issue raised by a very interesting comment regarding my previous blog, “The Brain in a Bucket.”

So I’ve taken the liberty of posting the comment here (hoping that’s OK in blog etiquette; still learning as I go), and then responding. Here it is:

I was pondering your statement that long term meditators show a thickening in certain areas of the brain. As I understand it, the volume of the skull is fixed in adults. This would seem to require that if one part thickens, another part must be reduced. I am curious as to whether anyone has considered what the implications of a loss of volume in these other areas might be. I enjoyed your article, and look forward to more on the topic of neurology and meditation.

While the size of the skull is indeed fixed in adulthood, we can both lose gray matter volume due to the normal effects of aging and gain it through mental training of one kind or another. For instance, one study showed that the hippocampus (really hippocampi, since there is one on each side of the brain, but convention is usually to refer to neural regions in the singular), of London taxi drivers is thicker after their training, which makes sense since the hippocampus is deeply involved with spatial memory.

But the size of these changes in volume is very small, so they do not “bump up against” the skull. For example, the increased thickness in the brains of meditators – seen in one of the cooler studies in this field – amounted – to about 1/200th of an inch. This may not seem like much but is a BIG change in the density of synaptic networks when you can fit about 5000 synapses in the width of a human hair.

The point is that small changes in daily activities – meditating instead of sleeping in, driving a cab instead of working in an office – can make changes in the brain that seem small but actually create big changes in the mind. And that fact opens the door to amazing opportunities.

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Rick Hanson, Ph.D., is a neuropsychologist and founder of the Wellspring Institute for Neuroscience and Contemplative Wisdom. A summa cum laude graduate of UCLA, he teaches at universities and meditation centers in Europe, Australia, and North America. His work has been featured on the BBC and in Consumer Reports Health, U.S. News and World Report, and other major magazines.